Discovery of DNA as genetic material Flashcards
What was known prior to the experiments that proved DNA was genetic material?
-Genes were known to be associated with specific characters but the nature of them were unknown.
-Genes were known to be carried on chromosomes
-Chromosomes contain DNA and proteins
-Composition of DNA was known but thought to be too simple to carry genetic material
What was the criteria of a molecule that is a carrier of genetic material?
Ability to store, transmit and maintain genetic info but with the capacity to change
What was Fredrick Griffith`s experiment
(1928) One of the first experiments suggesting bacteria are capable of transferring genetic info through process known as translation.
What bacteria did Fredrick Griffith use in his experiment?
Streptococcus pneumoniae
What was the outcome of Fredrick Griffith’s experiment?
One mouse was infected with type R nonvirulent bacteria - survived
One was infected with type S virulent bacteria - died
One was infected with heat-killed type S (heat got rid of capsule so got rid of virulence) - survived
One was infected with type R and heat killed type S - died
Why did the mlouth die from being infected with the R strain and heat killed S strain?
The R strain took the DNA from the heat killed S strain and changed it into an S strain which killed the mouse
What was the Avery-MacLeod-McCarthy experiment?
(1944) Demonstrated that DNA was the material causing bacterial transformation
What were the biomolecules in question in the Avery-MacLeod-McCarthy experiment?
RNA, Protein, DNA, Lipid, Carbohydrates
How did they test these biomolecules?
They used the heat killed virulent strain bacteria and added an enzyme ( rnase, protease, dnase, lipase or carboase).
Then added the treated samples to cultures of R strain bacteria
What was the outcome of the Avery-MacLeod-McCarthy experiment?
The cultures treated with all the enzymes except DNase contain transformed S strain bacteria meaning without the DNA present in the sample, the R strain was not able to adapt to gain the virulence of the S strain as the genetic info wasnt present
What was Hershey and Chases’ experiment?
(1952) Confirmed DNA as genetic material using bacteriophage T2
What 2 chemicals did Hershey and Chase use in their experiment?
Sulphur and Phosphorus
Sulphur marked the protein capsule
Phosphorus marked the DNA core
What are the results of the Hershey-Chase Experiment?
The radioactive sulphur is found in the supernatant (not in the cell)
The radioactive phosphorus is found in the cell fraction from which a new generation of infective phage can be isolated
What is the conclusion of the Hershey-Chase Experiment?
The active component of tze bacteriophage that transnmits the infective characteristic is the DNA.
Thus there is a clear correlation between DNA and genetic info
